- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Correlative optical and X‐ray imaging of strain evolution during Double Torsion Fracture Toughness measurements in shale
摘要： Mode-I Fracture Toughness, KIc, was measured in six shale materials using the double torsion technique. During loading, crack propagation was imaged both using twin optical cameras, and with fast X-Ray radiograph acquisition. Samples of Bowland, Haynesville, Kimmeridge, Mancos, Middlecliff and Whitby shales were tested in a range of orientations. The measured fracture toughness values were found to be in good agreement with existing literature values. The two imaging techniques improve our understanding of local conditions around the fracture tip, through in-situ correlation of mechanical data, inelastic zone size and fracture-tip velocity. The optical Digital Image Correlation (DIC) technique proved useful as a means of determining the validity of individual experiments, by identifying experiments during which strains had developed in the two ”rigid” specimen halves. Strain maps determined through DIC of the optical images suggest that the scale of the inelastic zone is an order of magnitude smaller than the classically used approximation suggests. This smaller damage region suggests a narrower region of enhanced permeability around artificially generated fractures in shales. The resolvable crack-tip was tracked using radiograph data and found to travel at a velocity around 470 m.s?1 during failure, with little variation in speed between materials and orientations. Fracture pathways in the bedding parallel orientations were observed to deviate from linearity, commonly following layer boundaries. This suggests that while a fracture travelling parallel to bedding may travel at a similar speed to a bedding perpendicular fracture, it may have a more tortuous pathway, and therefore access a larger surface area.
关键词： shale materials,fracture tip velocity,Double-torsion fracture toughness,optical digital image correlation,crack-mouth opening displacement,radiograph imaging
更新于2025-09-09 09:28:46
-
Consequences of Ultra-Violet Irradiation on the Mechanical Properties of Spider Silk
摘要： The outstanding combination of high tensile strength and extensibility of spider silk is believed to contribute to the material’s toughness. Thus, there is great interest in engineering silk for biomedical products such as suture or implants. Additionally, over the years, many studies have also sought to enhance the mechanical properties of spider silk for wider applicability, e.g., by irradiating the material using ultra-violet radiation. However, the limitations surrounding the use of ultra-violet radiation for enhancing the mechanical properties of spider silk are not well-understood. Here, we have analyzed the mechanical properties of spider silk at short ultra-violet irradiation duration. Specimens of spider silk were subjected to ultra-violet irradiation (254-nm wavelength, i.e. UVC) for 10, 20, and 30 min, respectively, followed by tensile test to rupture to determine the strength (maximum stress), extensibility (rupture strain), and toughness (strain energy density to rupture). Controls, i.e., specimens that did not received UVC, were also subjected to tensile test to rupture to determine the respective mechanical properties. One-way analysis of variance reveals that these properties decrease significantly (p < 0.05) with increasing irradiation duration. Among the three mechanical parameters, the strength of the spider silk degrades most rapidly; the extensibility of the spider silk degrades the slowest. Overall, these changes correspond to the observed surface modifications as well as the bond rupture between the peptide chains of the treated silk. Altogether, this simple but comprehensive study provides some key insights into the dependence of the mechanical properties on ultra-violet irradiation duration.
关键词： bond crosslinks,bond scission,extensibility,toughness,strength
更新于2025-09-04 15:30:14